U.S. Pat. No. 4,280,881 teaches a method for separating indene from mixtures of same with aromatic mono-olefins by extractive distillation using polar organic liquids containing oxygen, sulfur or nitrogen. Such polar organic liquids include sulfolane, 2-pyrrolidone, gamma butyrolactone, ethylene carbonate, tetramethylene sulfoxide, epsilon-caprolactam, an N-lower alkyl-2 pyrrolidone and/or a di-lower alkyl sulfoxide.
U.S. Pat. No. 4,371,428 teaches a method for separating vinyl toluene from other alkenyl-aromatics by extractive distillation using polar organic compounds as extractant. Such polar organic compounds contain oxygen, sulfur or nitrogen and have an atmospheric boiling point between 185.degree. and 300.degree. C., and includes tetramethylene sulfoxide as well as various pyrrolidones and sulfolane.
Japanese J49086330 teaches a method for removing 9-10 carbon atom aromatic hydrocarbons from aromatic mixtures by distillation with NN dialkylamides, tetramethylene sulfoxide, nitrites, nitrobenzenes, phosphates, sulfolane.
"Liquid--Liquid Equilibrium Studies for Separation of Aromatics" Rawat, et al, J. applied Chem Biotechnol. 1976 26, 425-435. This Article reports the separation of benzene/heptane and toluene/heptane for 11 solvents. The article indicates that 1,3-propane sultone was the best solvent. Table 3 shows sulfolane and DMSO to be more selective than TMSO when used for the extraction of toluene from heptane.
SU 499256 reports that the efficiency of the separation of aromatic hydrocarbons from their mixtures with non-aromatic hydrocarbons by liquid phase extraction is improved, when cyclic sulfoxides of formula ##STR1## where n=3-5, or their mixtures with water, are used as extractants. The process is stated in its abstract as finding use in the separation of cracking products. Review of the text reveals, however, that only mixtures of heptane-toluene were investigated and used to demonstrate the process.